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Capital & Coast District Health Board 
 Surgery, Women and Children’s Directorate Policies, Procedures, Protocols, Guidelines 
 
 
 
 
Policy Facilitator: Jeremy Tuohy  
Version no  4 
Policy no. 
Authorised by: Executive Director  Clinical 
Issue Date:  5th March 2012 
W&CHD 
Surgery, Women & Children’s Directorate 
Review date: 5th March 2015   WC UT-01 
 
Antenatal diagnostic screening and 
testing for aneuploidy 
Related documents 
W&CHD PPPG documents: 
•  Anti-D Immunoglobulin administration and Kleihauer testing 
 
Other: 
New Zealand Genetic Services - Maternal serum test information sheet 
New Zealand Genetic Services - Maternal serum test request form (for bloods) 
The Royal Australian and New Zealand College of Obstetricians and Gynaecologists 
– Amniocentesis and chorionic villus sampling information sheet. 
 
Policy 
Chromosomal aneuploidy describes any variation in chromosome number that 
involves individual chromosomes as opposed to entire sets.  This is a major cause of 
perinatal morbidity and mortality and the diagnosis can have significant long-term 
consequences for both the infant and their family. 
Prenatal non-invasive screening and invasive diagnostic testing are carefully targeted 
to identify the majority of these cases.  Non-invasive screening is necessary in order 
to facilitate timely information and/or intervention in those pregnancies which are 
affected. 
This policy is to: 
1.  Inform all providers of maternity care about the current screening and 
diagnostic services which are available. 
2.  Enable all pregnant women who have a positive non-invasive screening test 
to be appropriately counselled by their lead maternity carer (LMC), hospital-
based midwife or medical personnel.   The woman must then be offered 
referral to the Maternal Fetal Medicine (MFM) Service at Capital and Coast 
District Health Board in a timely manner. 
 
Scope 
•  All WHS Obstetricians, Registrars, and Senior House Officers 
•  All WHS Midwives 
•  All Access holders 
• All 
Ultrasonographers 
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Antenatal diagnostic screening and testing for aneuploidy 
Page 1 of 4 
W&CHD WC UT-01          ID 2179 
Date printed from SilentOne  05/03/2012 
Regard printed versions of this document as out of date – The SilentOne document is the most current version 
Capital & Coast District Health Board 
 Surgery, Women and Children’s Directorate Policies, Procedures, Protocols, Guidelines 
 
•  All Cytogenetics laboratory personnel  
Indications for diagnostic testing 
Antenatal diagnostic testing for aneuploidy is indicated when: 
1.  There is a personal or family history of an inheritable chromosomal or 
genetic disorder. 
2.  A woman has been screened for aneuploidy by any of the currently 
available screening methods (see below) and has been identified as being 
‘at risk’. 
3.  When a fetal anomaly has been identified by ultrasound scan which is 
associated with an increased risk of aneuploidy. 
 
Non-invasive screening tests which are 
currently available. 
Maternal age 
Maternal age is a poor screening method for chromosomal aneuploidy.  The Ministry 
of Health recommends that women are not offered diagnostic testing on the basis of 
maternal age alone. 
Nuchal translucency 
Nuchal translucency is an effective screening method which is performed between 11 
and 13+ weeks gestation. This test is arranged by the LMC and is recommended for 
all women. 
This type of ultrasound screening should however be performed in a unit which 
demonstrates quality control and is preferably a member of the MFM screening 
programme which uses current software from the Fetal Medicine Foundation, in 
London. 
Maternal serum screening 
Maternal serum screening is another effective screening method,  the test is now 
funded by the New Zealand government.  MSS1 consists of testing for PAPP-A and 
hCG at 9 to 14 weeks. The MSS2 consists of testing for Inhibin A, hCG, Oestriol and 
AFP at 14 to 20 weeks. The MSS1 is performed as part of the combined test. The 
Ministry of health has recommended the combined test as the primary screening 
method. The MSS2 is recommended for those women who are too far advanced in 
gestation for a combined screen. 
Combined testing 
Combined testing consists of a combination of nuchal translucency testing at 11 to 14 
weeks and first trimester maternal biochemistry . The risks from the maternal age, 
nuchal translucency, presence of the nasal bone and maternal biochemistry are 
combined to give a single risk. At risk of more than 1 in 300 is considered “high risk” 
and warrants referral for an amniocentesis. 
___________________________________________________________________________________ 
 
Antenatal diagnostic screening and testing for aneuploidy 
Page 2 of 4 
W&CHD WC UT-01          ID 2179 
Date printed from SilentOne  05/03/2012 
Regard printed versions of this document as out of date – The SilentOne document is the most current version 
Capital & Coast District Health Board 
 Surgery, Women and Children’s Directorate Policies, Procedures, Protocols, Guidelines 
 
Invasive testing 
Any woman who has a positive non-invasive screening test (1:300 or greater) must 
be offered referral to the MFM service in a timely fashion.  If the woman declines 
referral this should be clearly documented in her hospital medical records and signed 
by the woman. 
The type of invasive testing that will be offered to women depends largely upon the 
gestation at which the woman is referred.  Chorionic villus sampling (CVS) is offered 
from 11+ week’s gestation and amniocentesis is offered from 15+ weeks. 
The referral process 
•  The referring practitioner is responsible for informing the woman about the 
need for referral and explaining why invasive testing is indicated. 
•  All referrals for invasive testing will be triaged by the MFM specialists.  The 
MFM service will decide which invasive tests are appropriate for the woman.  
The circumstances and the timing of these tests will also be decided by the 
MFM service. 
•  If a woman declines invasive testing this will be clearly documented in the 
woman’s hospital medical records. 
Blood tests to be organised by the referring LMC 
A copy of the woman’s antenatal bloods and her blood group must accompany the 
referral form, as the MFM service will not be able to schedule an appointment until 
this information has been made available. 
Discussion and consent process 
Written consent will be obtained prior to any invasive procedure being performed. 
 
Chorionic villus sampling: 
Those women who undergo invasive testing prior to 14 weeks will be offered CVS.  
This procedure is usually performed via the trans-abdominal route, but it may also be 
performed trans-vaginally. 
The trans-abdominal route is sometimes considered unsuitable once the location of 
the placenta has been verified. 
Trans-abdominal technique 
• Sterile 
technique. 
•  The placenta is located using ultrasound. 
•  A 20 gauge needle is inserted into the uterus under direct ultrasound 
visualisation. 
•  Aspiration of the chorionic villi is achieved using negative pressure in a 20 to 
30 millilitres syringe. 
___________________________________________________________________________________ 
 
Antenatal diagnostic screening and testing for aneuploidy 
Page 3 of 4 
W&CHD WC UT-01          ID 2179 
Date printed from SilentOne  05/03/2012 
Regard printed versions of this document as out of date – The SilentOne document is the most current version 
Capital & Coast District Health Board 
 Surgery, Women and Children’s Directorate Policies, Procedures, Protocols, Guidelines 
 
•  The adequacy of the sample is assessed by the operator, the MFM 
coordinator or the cytogenetics laboratory. 
•  Two attempts are acceptable. Further attempts may be required, but are 
discouraged as this leads to a higher rate of miscarriage. 
 
Trans-vaginal technique 
• Sterile 
technique. 
•  The woman is placed into lithotomy. 
•  The placenta is located using ultrasound. 
•  CVS forceps are introduced into the cervix under direct ultrasound 
visualisation. 
•  Two attempts are acceptable. Further attempts may be required, but are 
discouraged as this leads to a higher rate of miscarriage. 
 
Amniocentesis: 
Amniocentesis is the preferred method of invasive screening if the woman is more 
than 15 weeks pregnant. 
• Sterile 
technique. 
•  The amniotic fluid is located using ultrasound. 
•  A 22 gauge needle is inserted into the uterus under direct ultrasound 
visualisation. 
•  Between 10 and 20 millilitres of amniotic fluid is required 
•  Two attempts acceptable. Further attempts may be required, but are 
discouraged as this leads to a higher rate of miscarriage. 
 
Analysis of the CVS and amniocentesis samples 
•  All samples will be analysed using GTG-banding after standard culture.  
These results are usually available within 12 to 14 days of the invasive 
procedure; the PCR results are available within 48 hours. 
•  Women who undergo invasive testing for aneuploidy on the basis of age 
alone will not be offered rapid analysis of their sample. 
•  CVS samples may be analysed using a direct preparation method, which 
allows for a rapid full karyotype where appropriate after discussion with the 
cytogenetics laboratory. 
 
Disclaimer: This document has been developed by Capital & Coast District Health 
Board (C&C DHB) specifically for its own use.  Use of this document and any 
reliance on the information contained therein by any third party is at their own risk 
and C&C DHB assumes no responsibility whatsoever. 
 
 
___________________________________________________________________________________ 
 
Antenatal diagnostic screening and testing for aneuploidy 
Page 4 of 4 
W&CHD WC UT-01          ID 2179 
Date printed from SilentOne  05/03/2012 
Regard printed versions of this document as out of date – The SilentOne document is the most current version